1. Field of the Invention
This invention relates to synthetic polyether thickeners and thickened aqueous systems containing them, particularly hydraulic fluids. The thickeners are prepared by reacting conventional polyether polyols with alpha-olefin epoxides having an average of from 6 to 12 total carbon atoms at effective epoxide to hydroxyl ratios which will produce thickeners with the desired properties.
2. Description of the Prior Art
Thickeners are known which can operate under severe shear forces, such as vane and gear pumps operating at pressures of 2000 psig and above. Examples of such thickeners are conventional polyether polyols (polyoxyalkylene polymers) having a molecular weight of approximately 10,000 to 50,000. The problem with these thickeners is that it takes large concentrations (at least 15 percent and usually more than 20 and 30 percent) to produce sufficient thickening efficiency.
Higher molecular weight thickeners such as gums and cellulose derivatives have excellent thickening efficiency, but are not shear stable even at lower operating pressures.
In an effort to solve the problems with the prior art thickeners, associative polyether thickeners as described in U.S. Pat. No. 4,411,819 were created. Although these thickeners have excellent thickening efficiency and work well in piston pumps operating at pressures of 2000 psig, they are not effective for fluids which are subject to higher shear forces, for instance, shear forces found in vane pumps and gear pumps operating at 2000 psig and above.
Herein is described a thickener which will not only operate in a vane or gear pump at 2000 psig, but will do so at a concentration which is economical to use.